In this observational study estimation of anesthetic depth by anesthesiologists is compared with the EEG based monitoring Narcotrend®. 10-20 voluntary anesthesiologists of the Kepler University Hospital, unfamiliar with EEG-monitoring during anesthesia, assess depth of anesthesia (moderate, deep or light level) during a steady-state period by clinical signs and measured or calculated concentrations of anesthetics. Concurrently Narcotrend® provides data of anesthetic depth (index, stadium) blinded for the anesthesiologist. Each anesthesiologist is included 30 times during study period. The aim of this study is to define conformity between subjective and objective assessment of narcotic depth. In the cases of divergence data of the patient (age, body mass index, comorbidity…), data of the anesthesiologist (age, years of practice…), data of anesthesia (balanced anesthesia, target controlled infusion, endtidal concentration of volatile anesthetic…) and data of the operation (eye surgery, cardiac surgery…) will be analyzed by statistics with regard to underlying or concomitant factors. These findings could help to develop recommendations in the use of EEG-processed monitoring to improve subjective assessment and facilitate an adequate depth of anesthesia to be provided for every patient.